At present, the Type-C, as an emerging Universal Serial Bus (USB) interface standard under the support of the USB-PD protocol, can provide a high data transmission speed, a high online power supply capability and a simple and convenient system connection, and supports a simultaneous transmission of USB3.1 data and video data of multiple types such as the DisplayPort (DP), the High Definition Multimedia Interface (HDMI) and the Mobile High-Definition Link (MHL). According to the USB-PD specification, a Type-C connection between an upstream device and a downstream device is implemented by performing a communication on a Configuration Channel (CC) based on a Biphase Mark Coding (BMC) mechanism, and a rising edge or falling edge of a to-be-transmitted waveform obtained by the BMC is specified strictly in the USB-PD protocol. However, due to an indeterminacy of a parasitic parameter of a Type-C connection system, the rising edge or falling edge of the to-be-transmitted waveform should be designed as regulatable, so as not to depend on a system connection attribute while conforming to the USB-PD standard.
Referring to FIG. 1, a traditional BMC transmitter having a conversion speed control function is shown. Signals d1 to dn at an equal interval are obtained by performing an n-stage clock sampling on input data di (the interval is equal to the clock period Tck). Then, the signals d1 to dn at the equal interval are respectively transmitted to buffers BUF1 to BUFn to switch on the n BUFs successively to drive output, thereby generating the output waveform with controlled rising edge or falling edge, as shown in the upper part of FIG. 2. The conversion speed can be changed by changing a clock frequency, i.e., the clock period Tck. The lower part of FIG. 2 shows waveforms corresponding to a light load and a heavy load. Apparent rising edge steps and falling edge steps can be seen in the figure. The steps are filtered by a filter in practices, to obtain a smooth rising edge and a smooth falling edge. However, such traditional BMC transmitter has disadvantages as follows. As components of a BMC transceiver, a BMC transmitter is a digital circuit while a receiver is an analog circuit. Therefore, in design, a power source and ground for the BMC transmitter should be isolated from a power source and ground for the receiver, to prevent a mutual influence between power source systems of the digital module and the analog module. In the structure of the traditional BMC transmitter (as shown in FIG. 1), the regulation of the rising edge or falling edge are controlled by several clocks at an equal interval or by several stages of sampled data. However, what are driven by the equal-interval data or clocks are digital buffers, thereby causing a large noise of a power switch and consuming a large chip area and power.